The present invention relates generally to electron sources and more particularly to asymmetrical field emitters on a substrate.
In numerous applications, solid state field emitters are replacing electron guns. There are many ways to build a solid state field emitter. FIGS. 1A-C show conceptually the process to build one type of field emitters. For that process, after the formation of the basic structure as shown in FIG. 1A, an emitter material is deposited as shown in FIG. 1B. Then the emitter material on top of the gate is removed to form the field emitter as in FIG. 1C. The diameter of the hole exposing the emitter is on the order of a few microns, and its proximity to the emitter has to be very well controlled. Another very important parameter is the size of the tip of the emitter. The tip should be very sharp in order to create a high electric field. Unfortunately, it is difficult to make very sharp tips based on the process shown.
FIGS. 2A-C show conceptually another process to make a field emitter. This method is based on a single crystalline silicon substrate. First, a part of a silicon substrate is masked as shown in FIG. 2A. Then the substrate is etched. Due to the anisotropic nature of the single crystalline silicon, a pyramid-shaped structure is formed under the mask. The mask is then removed leaving the pyramid-shaped structure to be the emitter, as shown in FIG. 2C. The pyramid can then be sharpened by oxidation. This type of field emitters depends on a single crystalline silicon substrate, which is quite difficult to have a substrate size large enough for applications in areas such as flat panel displays.
It should be apparent from the foregoing that there is still a need for a field emitter with a very sharp emitter in close proximity to its gate. Further, the field emitter should not be limited to be on a single crystalline silicon substrate.